Since Firefox 89 and the new floating tabs, I used this theme. However, at first the tab outline was the same color as the tab itself, which in my opinion looks a lot better than the current one (black tab, blue outline). This theme is already very good-looking, could be even better if you made the tab outline the same color as the tab itself.

Theme itself is quite nice. Only one thing is bothering me. In some occasions it is too dark. Active tabs are hard to identify and in the adress field you cant see if something is marked. Its just black on black.